Petroleum products contain relatively high levels of sulfur, in the form of organic sulfides, organic disulfides, thiols, and aromatic compounds like thiophene, benzothiophene, etc. For more reasons, it is desirable to lower the amount of sulfur in said products. Sulfur poisons the catalysts that are used in reforming of crude hydrocarbons, or in catalytic converters of the car engine. Reducing the sulfur level in gasoline has further a beneficial effect in reducing the corrosion of the engine components. A strong incentive to lower the sulfur levels in fuels comes from environmental considerations. Sulfur oxide emissions from the car engines contribute to acid rains, whereas the poisoning of the catalytic converters by sulfur leads to increased emissions of nitrogen oxide, carbon monoxide and unburned hydrocarbons. The specification for diesel fuel is about 500 weight parts of sulfur per million weight parts of fuel (ppm). The US average gasoline has about 350 ppm sulfur. It is expected that the US and EU sulfur specification will be less than 50 ppm for gasoline after 2005. It is therefore desirable to achieve ultra-deep desulfurization of commercial fuels, even down to 1 ppm sulfur or less.
Petroleum hydrocarbon based liquids, such as gasoline, are one of the preferred fuel sources being considered for future Fuel Cell Vehicles (FCV's). Other fuel choices, such as methanol or hydrogen, require building new manufacturing and distribution infrastructure system, which will be very expensive. Utilizing gasoline takes advantage of the existing fuel distribution and retail infrastructure. However, with even state-of-the art fuel cell systems, sulfur at 1 ppm can be potentially poisoning to the fuel processor and the fuel cell stack, which would cause reduced fuel efficiency. An on-board sulfur trap, which is capable to remove sulfur to less than 1 ppm may be required to safe guide the operation of fuel processor and stack.
There are two key requirements for an on-board sulfur trap. The first one is the sulfur capacity of a given sulfur trap material. Higher capacity means a longer lifetime of the trap. For example, for a trap of 1.5-liter, a sulfur capacity of 0.5 g/cc % would run for about 5,000 miles before replacement on a 30 ppm sulfur gasoline. But, if the sulfur capacity is 2 g/cc %, the trap would last for more than 16,000 miles. Currently, no prior art has disclosed any materials that achieve a sulfur capacity of greater than 1.5 g/cc % for removing sulfur from 30-ppm sulfur pump gasoline to 1 ppm or less.
The second issue related to on-board application is the material reactivity. For a given fuel processor, it requires a certain fuel rate to meet its maximum power level. This requirement can be met by either increasing the amount of trap material (trap size increase) or using more reactive sulfur trap material. A highly reactive material provides a number of advantages for on-board applications. It reduces weight, volume, and is easier to handle.
The art discloses a number of processes for removing the sulfur compounds from hydrocarbon streams; the more practical of which comprise a nickel catalyst. U.S. Pat. No. 5,807,475 describes an adsorbent for desulfurization of gasoline based on nickel-exchanged zeolite. After 16 h of treatment, the sulfur content of naphtha decreased to 200 ppm. U.S. Pat. No 6,254,766 describes a sorbent comprising nickel deposited on an inorganic support obtained by mixing of zinc oxide, silica and alumina. Said sorbent lowers the sulfur content in gasoline from 310 ppm to 30 ppm at 350° C. in the presence of hydrogen.
Multi stage processes, using different catalysts and different conditions at each stage, reach lower levels of sulfur. U.S. Pat. No. 5,322,615 describes a method for removing sulfur from hydro-treated naphtha to ultra-deep desulfurization level of less than 0.02 ppm in three stages, comprising treatment with nickel, and treatment with hydrogen in the presence of platinum, while employing temperatures up to 450° C. and pressures up to 35 atm. U.S. Pat. No. 5,114,689 describes a three-stage process for ultra-deep desulfurization of naphtha to a level of less than 0.02 ppm, comprising treatment with 4% to 54% nickel dispersed in amorphous silica bound with alumina in the presence of hydrogen, treatment with 0.2% platinum on alumina in the presence of hydrogen, and treatment with potassium on alumina, employing temperatures 260-345° C. U.S. Pat. No. 5,106,484 describes a three-stage process for lowering the sulfur content in hydro-treated naphtha to 0.1 ppm, comprising treating said naphtha with nickel, and then with hydrogen in the presence of manganous oxide, employing temperatures 400-600° C. and pressures up to 20 atm. U.S. Pat. No. 4,634,515 describes a nickel catalyst, consisting of at least 50% elemental nickel dispersed in alumina, used in a three stage process including naphtha reforming, wherein 0.5 ppm of sulfur is reached in said naphtha. U.S. Pat. No. 4,925,549 describes a method for removing sulfur to less than 0.1 ppm in two stages, comprising treating with hydrogen in the presence of Zn/Al2O3 catalyst, and contacting with barium exchanged zeolite.
Tawara K. et al. [Sekiyu Gokkaishi 43 (2000) 114-120] describe a sorbent of nickel deposited on the support made of ZnO—Al2O3, allowing to remove the sulfur compounds from kerosene from a level of 62 ppm down to less than 1 ppm in one stage, while employing hydrogen treatment at a temperature of 325° C.
It appears that the state of art in desulfurization of hydrocarbon feedstocks does not allow to reach the sulfur level of 1 ppm or less in absence of hydrogen, and at temperatures lower than 250° C. It is therefore an object of the present invention to provide a new process for ultra-deep desulfurization of hydrocarbon streams.
It is an object of the present invention to provide a new process for desulfurization of hydrocarbon streams enabling to achieve the sulfur level of 1 ppm or less at temperatures lower than 250° C.
It is another object of the present invention to provide a process for ultra-deep desulfurization of hydrocarbon streams enabling to achieve the sulfur level of 1 ppm or less in absence of hydrogen.
It is still another object of the present invention to provide a new process for ultra-deep desulfurization of commercial fuels enabling to achieve The sulfur level of 1 ppm or less in one stage.
It is further an objective of this invention to provide a highly reactive adsorbent for desulfurization of hydrocarbon streams.
It is further an object of this invention to provide a high capacity adsorbent for desulfurization of hydrocarbon streams.